Automatic landing systems for aircraft



Nov. 12, 1963 G. s. BISHOP 3,110,458

AUTOMATIC LANDING sysTEMs FoR AIRCRAFT Filed oct. so', 1961 mvENroR GEoFFREY STANLEY alsHoP United States Patent O 3,110,458 AUTOMATIS LANDING SYSTEMS FOR AIRCRAFT Geoirey Stanley Bishop, Stopsley, Luton, England,

assignor to Elliott Brothers (London) Limited, London,

England, a company of Great Britain Filed Oct. 30, 1961, Ser. No. 148,610 Claims priority, application Great Britain Nov. 1, 1960 14 Claims. (Cl. 244-77) This invention relates to improvements in automatic landing systems for aircraft.

When an aircraft is flown in a cross wind with its wings level it crabs, i.e. thedirection of its travel over the ground differs from the direction in which the fuselage is pointing by an angle know-n as the crab or drift angle.

If, under these conditions, an aircraft is flying down the l centre line of a runway preparatory t-o landing its wheels will not be pointing in the correct direction and so will experience an undesirable side load at the i-nstant of touchdown.

A pilot minimises the side lo-ad by one of two methods (or a combination of the two). One is to decrab or kick olf Ithe drift during the last few seconds before touchdown by applying rudder to align the aircraft heading with the runway, while relying on the aircraft inertia to maintain its direction of travel substantially unchanged over this short time. The other method is to sideslip the aircraft, i.e. to y deliberately banked so that the sideslip produced by the bank angle substantially Acompensates for any tendency to drift due to wind, and thus to keep both the aircraft heading and track simultaneously and continuously aligned with the runway during the final approach and landing.

For large transport aircraft in the approach -coniiguration, aerodynamic lags are likely to be too great to permit the decrabbing manoeuvre to be carried out in the short time required to avoid an unacceptable sideways drift. Also, the manoeuvre should begin at a set time before touchdown, the time of which is difficult to predict accurately.

Basically, there are two flying controls, rudder and aileron, available for lateralcontrol of a conventional aircraft, and with these it is possible to satisfy two independent conditions continuously. In the first method these two conditions are (a) aircraft tracking along runway centre line, (b) wings level, until a tew seconds lbefore touchdown, when condition (a) becomes aircraft heading along runway centre line. In the second method, the two conditions are ('a) aircraft tracking along runway centre line, (b) aircraft heading along runway centre line, and this mode of control is used for a long enough time Ibefore vtouchdown to ensure that the conditions are set.

It is an object of the present .invention to provide an improved automatic landing system for aircraft whereby an aircraft is landed by the second method referred to above.

According to the present invention, an automatic aircraft landing system comprises means for deriving control signals as functions of the departure of the aircraft heading angle from the runway angle `and of the lateral displacement of the aircraft relative to the runway and means Ifor controlling the aircraft rudder and ailerons in response to the contro-l signals in the sense to reduce such ycon-trol signals to zero by causing the aircraft to head and track along the runway banked at an angle sufficient to compensate for any tendency to drift due to the Wind.

More particularly, the invention provides an automatic aircraft landing system comprising means for deriving -a first control signal as a function of the bank angle of the aircraft, means for deriving a second control signal as a form Kzqb where K2 is a Igearing factor.

ICC

Patented Nov. 12, 1963 function of the departure of the `aircraft heading angle from the runway angle, means for deriving a third control signal -as an integral function of such departure, means for deriving a fourth control signal as a function of the lateral displacement of the aircraft relative to the runway, means -for deriving a fifth control signal -as an integral function of such displacement, rudder control means responsive to the second, third, fourth and fifth control signals to control the rudder in the sense to reduce the second control sign-al to zero and cause the aircraft to head along the runway and aileron control means responsive to the first, second, fourth and fifth signals to control the ailerons in the sense to reduce the fourth control signal to Zero and cause the Vaircraft to assu-me or maintain 4a bank angle sufficient to compensate for any tendency to drift due to wind.`

More specifi-cally stated, the invention provide-s an automatic landing system for aircraft comprising means for deriving aileron control signals in the form Klp, Kgq, K3(1//-1pD), Knr and K5fedt, where K1, K2, K3, K4 and K5 are gearing factors and p is the roll rate of the Iaircraft, g5 is the bank angle, gb is the heading angle, ,Z/D is the demanded heading or runway angle, a is the lateral displacement of ythe aircraft relative to the runway and t is time, aileron control means fo-r causing the ailerons to assume an aileron angle 5 which is a function `of the sum of the aileron control signals, means for deriving rudder control signals in the forni Ksr, Knip-gn), Kga, Kgfadt and K10f(\,*\/D)df, Where K6, K7, K3, K9 K10 'are gearing factors and r is the yaw rate, and rudder control means responsive to the rudder control signals to cause the rudder to assume a rudder angle s which is a function of the sum of the rudder control signals.

One embodiment of the invention Will now be described by Wray of example, reference being made to the `accompanying block schematic diagram of an automatic landing system for aircraft.

In this example, the aircraft ailerons 1 are controlled by an `actuator or actuators 2 under the control of la part 3 of `an autopilot computer. The rudder or rudders 4 is or are controlled by an actuator or actuators '5 under the control of another part 6 of the autopilot computer. A lroll rate gyroscope 7 is providedy to derive a control signal 'as a :function of the roll rate p` of the aircraft, this control signal being amplified by an ampliiier 8 to provide a control signal to the 3 of the autopilot computer in the form K1 p where K1 is a gearing factor.

A vertical gyroscope 9" is provided to derive a control signal as a yfunction of the bank angle qb of 1the aircraft, this control signal being amplilied by an amplifier 10 to provide a control signal to the autopilot part 3 in the A directional gyroscope or gyrocompass 11 is provided to derive a si-gnal as a function of the aircraft heading and Ithisl signal is supplied to a course deviation indicator 12 or other instrument having a facility for the pilot to set in the runway heading angle Ito derive a control signa-l which is a function of the departure of the aircraft heading tb from the runway heading gI/D. This last-mentioned control signal is supplied to both amplifiers 13 and 14 and to an integrator 15. The amplifier 13- provides a control signal to the autopilot pant 3 in the form ICSW-3h13) and the amplifier 14 provides a control signal to the autopilot part 6 in the form Kqp-r/fn) where K3 and K7 are gearing factors. The output of the integrator 15 is amplified by an amplifier 16 to provide a control signal to the autopilot part 6 in the form KwfW-ipwdt.

A device 17 is provided to provide a signal which is a func-tion of the lateral displacement oof the aircraft relative to the runway centre line. This device 17 may, for example, be an I.L.S. localiser receiver, a leader cable receiver or a leader beacon receiver or a combination of these. This displacement signal is supplied both to arnplifiers 18 and 19 and to an integrator 20. The amplifier 1S provides a control signal to the autopilot part 31v in the form Kga and the amplifier 19y provides a control signal to the autopilot part 6 in the form Kga, where K4 and K8 are gearing fac-tors. The integrated output from the integnator 2t? is supplied to amplifiers 2.1 and 22, the amplifier 21 supplying a control signal to the autopilot part 3 in the form Kfm't and the amplifier 22 supplying a control signal to the autopilot part `6 in the form Kgfadt. A yaw rate gyroscope 23 is provided to derive a signal as a function of the yaw rate r of the aircraft, this signal being fed to an amplier 24 the output of which is supplied to the autopilot part 6 in the form Ker where K6 is a gearing factor.

Position feedback is provided from the ailerons 1 to the autopilot part 3 and stalibising feedback is provided from the actuator 2 to the autopilot part 3 so that the ailerons 1 follow the command of the autopilot part 3 according to the equation Position feedback is provided yfrom the rudder 4 to the autopilot part `6 and stabilising feedback is provided from the actuator '-5 to the autopilot part 6 so that the rudder follows the command of the autopilot according to the equation lt -will be appreciated that although these gearing factors have been described as being obtained from amplifiers 8, 1G, 13, 14, 16, 18, 19, 2&1 and 2v2, they may, in practice, be derived within the autopilot parts El` and 6 and/or from parametric gain adjusting devices. Additionally, some or all the rudder control signals derived from the course deviation indicator 12v, the 4device 17 and the integrator may be supplied to the autopilot part 6 from the autopilot part 3 as indicated by the dotted line 25, as will be Y understood.

Means 3u* responsive to aircraft altitude, e.g. a barometric altimeter or a radio altimeter, is provided to switch the integrator 15 from the off to the on condition or, in other words, to vary the K10 gearing factor from 0 to its selected value at a selected altitude as the aircraft approaches the runway. This means may also be such as to control the amplifier 1d to increase K7 from a first to a second selec-ted value. This altitude responsive means Vmust respond a suflicientvtirne, e.g. at least one minute,

before touchdown to allow all the controls to operate in 4the intended manner and to be observed to do so Iand usually should be set to operate at a height not less than 200 ft. Means may also be provided to modify or disconnect the control signals automatically at or just prior to touch-down.

The ope-ration of the system described is substantially as follows:

. Before entering upon the landing phase the aircraft Will normally be controlled by the autopilot in response to radio guidance signals possibly derived from the device 17. The control equations will be as set out above except y d that K10 will be zero and K, may have the first selected value. At a selected altitude, e.g. at least 20G ft., the integrator is switched on and K7 may be increased to its second selected value. Rudder is thus applied to yaw the aircraft towards the runway. The resultant yaw applies aileron through the K3 term and the aircraft banks into the Wind. When a steady condition is obtained, the outputs of integrators 15 and Zit are no longer changing so that the desired conditions, i.e. uz() and 1,//-1//D=O, are achieved, and the aircraft is iiying with its heading and track aligned along the runway centre line and banked into the wind at an angle sufficient to compensate for any drift due to wind.

lt -will be appreciated that although the invention has been described in its application to a position command system, it can also be used with a rate-rate system, i.e. one in which the rates of change of the aforementioned demand signals are made to demand control surf-ace rates. For instance, the position feedback from the ailerons 1 to the autopilot pant Ity can be omitted, thus converting the actuator Z into a rate actuator, the gyroscope 9 can be replaced by a rate gyroscope, the rate gyroscopes 7 and 23 can be replaced by angular accelerometers, the integrators 15 and 2% can be omitted and dilferentiators introduced as indicated in dotted lines at 26 and 27.

lt is also possible on some aircraft to omit the autostabilisation terms from the gyroscopes 7 and 23, or to replace them with the outputs from the vertical gyrosco-pe 9 and gyrocompass '11, passed through differentiators or other suitable filters. This applies equally to a position demand systemor a rate demand system.

What I claim is:

l. An automatic aircraft landing system comprising means for deriving a first control signal as a function of the bank angle of the aircraft, means for deriving a second control signal as a function of the departure of the aircraft heading angle from the runway angle, means for deriving a third control signal as an integral function of such departure, means for deriving a fourth control signal as a function of the lateral displacement of the aircraft relative to the runway, means for deriving a fth control signal as an integral function of such displacement, rudder control means responsive to the second, third, fourth and fifth control signals to control the rudder in the sense to reduce the second control signal to Zero and cause the aircraft to head along the runway and aileron control means responsive to the first, second, fourth and fifth signals to `control the ailerons in the sense to reduce the fourth control signal to zero and cause the aircraft to assume or maintain a bank angle suicient to `compensate for any tendency to drift due to wind.

2. A system according to claim 1 wherein altitude responsive means is provided to switch said third signal deriving means from an inoperative condition when the aircraft altitude exceeds `a predetermined value to an operative condition when the aircraft altitude is less than said predetermined value.

3. A system according to claim 2 wherein said altitude responsive means is arranged Ito modify the functional relationship of said second -control signal to the departure of the aircraft heading angle from the runway angle to which the rudder control Ineans'responds from one relationship when the aircraft altitude exceeds said predetermined value to another relationship when the aircraft altitude is below 'said predetermined value.

4. A system according to claim 1 wherein the rudder control means includes a rudder computer device responsive to the rudder control signals and a rudder actuator operable by the yrudder computer device to control the rudder and the aileron control means includes an aileron computer ldevice responsive to the aileron control signals and an aileron actuator operable by the aileron computer device to control the ailerons.

5. A system according to claim 4 wherein a position loop is provided from the aileron `actuator to the aileron computer.

8. An automatic landing system for aircraft comprising means for deriving aileron control signals in the form KIp: 1(2(26: K3(1l r//D)a :[440 and 'KSIO-d: Where K1 K2,

K3, K4 and K5 are gearing factors and p is the roll rate` of the aircraft, gb is the #bank angle, tlf is the heading angle, i//D is the demanded heading or runway angle, a is the lateral displacement of the aircraft relative to the runway and t is time, `aileron control means for causing the ailerons to assume an aileron angle which is a function `of the sum of the aileron control signals, means for deriving rudder control signals in the form Ksr, Km0-50D), Kaff, Kgfadl, andiKwftib-iwdf, Where K6, K7, KB, K9 and K10 are gearing factors and r is the yaw rate, and rudder contr-ol means responsive to the rudder control signals to cause the rudder to `assume a rudder angle y which is a function of the sum of the rudder control signals.

9. A system according to claim 8 wherein `altitude responsive means is provided to make the rudder control signal represented by Klof(ip*i//D)dt equal to Zero when the aircraft altitude exceeds a predetermined magnitude.

10. A system according to claim 9 wherein the altitude responsive means is arranged to modify the value of K7 from one value when the aircraft altitude is less than said predetermined magnitude to `another Value when the aircraft altitude exceeds said predetermined magnitude.

11. A system according -to claim 8 wherein the functional relationship of the aileron angle to the aileron signals is in the form 6 l2. A system according to claim 8 wherein the functional relationship of the rudder angle to the rudder control signals is in the form 13. A system according to `claim 8 wherein the rudder control means includes a rudder computer device responsive to the rudder control signals and a rudder actuator operable by the rudder computer device to control the rudder and the aileron control means includes an aileron computer device responsive to the aileron control signals and an aileron actuator operable by the aileron computer device to control the ailerons.

I4. An automatic landing system for aircraft comprising means `for deriving aileron control signals in the form of Kip X295, Kaw-IPD), K4 and K5flfdf where K1, K2, K3, K4 `and K5 are gearing factors and p is the roll rate of the aircraft, p is the bank angle, 1]/ is the heading angle, ,l/D is the `demanded heading or runway angle, a is the lateral `displacement of the aircraft relative to the runway and t `is the time, aileron control means for causing the ailerons to assume an aileron angle where means for deriving rudder control :signals in the form KEI', K7(\/D), Kg', .Kgf'dt and K10f(tl/ l|/D)df, Where K6, K7, K8, K9 and K10 are gearing factors and r is the yaw rate, and rudder control means responsive to the rudder control signals to cause the rudder to assume a rudder angle gf where References Cited in the le of this patent UNITED STATES PATENTS 2,808,999 Chenery Oct. 8, 1957 

1. AN AUTOMATIC AIRCRAFT LANDING SYSTEM COMPRISING MEANS FOR DERIVING A FIRST CONTROL SIGNAL AS A FUNCTION OF THE BANK ANGLE OF THE AIRCRAFT, MEANS FOR DERIVING A SECOND CONTROL SIGNAL AS A FUNCTION OF THE DEPARTURE OF THE AIRCRAFT HEADING ANGLE FROM THE RUNWAY ANGLE, MEANS FOR DERIVING A THIRD CONTROL SIGNAL AS AN INTEGRAL FUNCTION OF SUCH DEPARTURE, MEANS FOR DERIVING A FOURTH CONTROL SIGNAL AS A FUNCTION OF THE LATERAL DISPLACEMENT OF THE AIRCRAFT RELATIVE TO THE RUNWAY, MEANS FOR DERIVING A FIFTH CONTROL SIGNAL AS AN INTEGRAL FUNCTION OF SUCH DISPLACEMENT, RUDDER CONTROL MEANS RESPONSIVE TO THE SECOND, THIRD, FOURTH AND FIFTH CONTROL SIGNALS TO CONTROL THE RUDDER IN THE SENSE TO REDUCE THE SECOND CONTROL SIGNAL TO ZERO AND CAUSE THE AIRCRAFT TO HEAD ALONG THE RUNWAY AND AILERON CONTROL MEANS RESPONSIVE TO THE FIRST, SECOND, FOURTH AND FIFTH SIGNALS TO CONTROL THE AILERONS IN THE SENSE TO REDUCE THE FOURTH CONTROL SIGNAL TO ZERO AND CAUSE THE AIRCRAFT TO ASSUME OR MAINTAIN A BANK ANGLE SUFFICIENT TO COMPENSATE FOR ANY TENDENCY TO DRIFT DUE TO WIND. 